Principles Of Seed Production 2uy2f

General Principles of Seed Production Production of genetically pure & good quality pedigree seed is a task requiring high technical skills & comparatively heavy finical investment. During seed production strict attention must be given to the maintenance of genetic purity & other qualities of seeds in order to exploit the full dividends sought to be obtained by introduction of new superior crop plant varieties. In other words seed production must be carried out under standardized & well organized conditions. GENETIC PRINCIPLES Deterioration of variety Genetic purity (trueness to type) of a variety can deteriorate due to several factors during production cycles. The best means to ensure genetic purity would be to overcome to the greatest possible extent the various factors responsible for genetic deterioration. The important factors of apparent & real deterioration. The important factors of apparent & real deterioration of variety as listed by Kadam (1942) are as follows:1. Developmental variation 2. Mechanical mixture 3. Mutation 4. Natural Crossing 5. Minor Genetic Variation 6. Selective Influence of Diseases 7. The Techniques of the Plant Breeder Of these mechanical mixtures, natural crossing & selective influence of diseases are the most important reasons for genetic deterioration of varieties during seed production, followed by raising the seed crop in areas outside their adaptation which may cause developmental variation & genetic shifts in varieties. 1. Developmental Variations:- When seed crops are grown in difficult

environment under different soil & fertility conditions or different climatic conditions or under different photoperiods or at different elevations for several consecutive generations the developmental variation may arise. To minimize such variations to occur in the varieties it is advisable to grow them in their areas of adaptation & growing season.

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2. Mechanical Mixtures:- This is the most important source of variety

deterioration during seed production. Mechanical mixtures may often take place at time of sowing, if more than one variety is sown with same drill; through volunteer plants of the same crop in the same field or through different varieties grown in adjacent fields; or during harvesting & threshing operations. Often the seed produced of all the varieties are kept on same threshing floor, resulting in considerable varietal mixtures. Secondly combining or threshing equipment is often contaminated with seeds of other varieties in augers, elevators etc. Further gunny bags, seed bins, elevators etc are also quite often contaminated with seeds of other varieties. To avoid this sort of mechanical mixture contamination it would be necessary to rogue the seed fields and practice the utmost care during seed production, harvesting, threshing & further handling. 3. Mutations:- This is not a

serious factor of varietal deterioration. In majority of cases it is difficult to identify or detect minor mutations. The mutant can be removed from seed plots to purify the seeds. In case of vegetatively propagated crops periodic increase of true to type stock would eliminate the deterioration effects of mutations.

4. Natural Crossing:- In sexually propagated crops natural crossing is

another most important source of varietal deterioration due to introgression to genes from unrelated stocks which can be only solved by prevention. The extent of varietal contamination depends upon the amount of natural cross-fertilization. The deterioration in variety due to natural crossing occurs due to the following 3 reasons:i) Natural crossing with undesirable type. ii) Natural crossing with diseased plant iii) Natural crossing with off-type plants In self fertilized crops, natural crossing is not a serious source of contamination & variety deterioration unless the variety is male sterile & is grown in close proximity to other varieties. But in Cross fertilized crops, natural crossing is the major source of genetic contamination. According to Bateman (1947) the extent of genetic contamination in seed fields due to natural crossing depends upon the following factors: i) The breeding system of species (ii) Isolation distance iii) Varietal mass (iv) Pollinating agent

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As the isolation between varieties is increased the contamination generally deceases, although there may be small amounts of contamination over wide distances. Isolation of seed crops, therefore is a primary factor in seed production of crop plants cross fertilized by wind or insects. The extent of contamination depends upon the direction of prevailing winds, no: of insects present & their activity, humidity & temperature at time of anthesis etc. In addition to these the mass of varieties involved is also important in the amount of contaminating influence. 5. Minor Genetic Variation:- Minor genetic variation may still exist even

in the varieties appearing phenotypically uniform & homogeneous at the time of their release. During later production of cycle some of these variations may be lost because of selective elimination by environment. To over come these De Hann (1953) has suggested yield trials of lines propagated from plants of breeder’s seed in the maintenance of self fertilized crop varieties. Minor genetic variability may be constant features in often cross fertilized crop species. Care during maintenance of nucleus & breeder’s seed is necessary in such cases. 6. Selective Influence of Disease:- The selective influence of diseases in

varietal deterioration is also of considerable importance. New crop varieties often become susceptible to new races of diseases often caused by obligate parasites & are out of seed programmes. Similarly vegetatively propagated stocks deteriorate fast if infested by viral, fungal & bacterial diseases. During seed production it is very necessary to produce disease free seeds/stocks. 7. Techniques of plant Breeder:- In certain instances serious instabilities

may occur in varieties due to cytogenetical irregularities not properly assessed in the new varieties prior to their release. Premature release of variety still segregating for resistance & susceptibility to disease or other factors may also be important in the deterioration of varieties. This could be looked upon as the factor of the variety testing programme In addition to the factors discussed above, other factors such as break down in male sterility, certain environmental conditions & other heritable variation may considerably lower the genetic purity.

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Maintenance of Genetic Purity During Seed Production The methods suggested by Horne (1953) and Hartmann & Kester (1968) may be used wholly or partly in part to maintain high levels of genetic purity during seed production. The various steps suggested by Horne (1953) to maintain varietal purity are as follows: a) Use of approved seed only in seed multiplication. b) Inspection & approval of fields prior to planting. c) Field inspection & approval of growing crops at critical stages for verification of genetic purity, detection of mixtures, weeds and for freedom from noxious weeds & seed borne diseases. Etc d) Sampling & sealing of cleaned lots. e) Growing of samples of potentially approved stocks for comparison with authentic stocks. The various steps suggested by Hartmann & Kester (1968) to maintain varietal purity are as follows: a) Providing adequate isolation to prevent contamination by natural crossing or mechanical mixtures. b) Roguing of seed fields prior to the stage at which they could contaminate the seed crop c) Periodic testing of varieties for genetic purity. d) Avoiding genetic shifts by growing crops in areas of their adaptation only. e) Certification of seed crops to maintain genetic purity & quality of seed. f) Adopting the generation system. g) Grow out test. The mechanism of maintaining genetic purity is further strengthened by the generation system. In this system, the seed production is restricted to four generations only. Starting from breeder’s seed, the seed can only be multiplied upto three more generations, i.e. foundation, ed & certified. The Important safeguards for maintaining genetic purity during seed production thus are:a) Control of seed Source: The use of seed of an appropriate class & from an approved source is necessary for raising a seed crop. Four classes of seeds, namely breeder’s, foundation, ed, certified are generally

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recognized in seed certification. The classes are given below as defined by the Association of Official Seed Certifying Agencies (AOSCA): Breeder’s Seed: It is seed or vegetative propagating material which is directly controlled by the originating or in certain cases, the sponsoring breeder or institution and which provides for the initial & recurring increase of foundation seed. Foundation Seed: foundation seed include seed stock so handled as to most nearly maintain specific genetic identity & purity and that may be designated or distributed by an agricultural experiment station. Production must be carefully supervised or approved by representatives of the station. Foundation seed is the source of all other certified seed classes, either directly or through ed seed. ed Seed: It is progeny of foundation or ed seed that is so handled as to maintain satisfactory genetic identity & purity and that has been approved and certified by a certifying agency. This class of seed should be of a quality suitable for production of certified seed Certified Seed: It is progeny of foundation, ed or certified seed that is so handled to maintain satisfactory genetic identity & purity and that has been approved & certified by certifying agency. b) Preceding Crop Requirements:

This has been fixed to avoid contamination through volunteer plants & also the soil borne diseases.

c) Isolation: The isolation of seed crops from various sources of

contamination is necessary requirement for raising seed crops. Contamination may be due to natural crossing with other varieties grown alongside & off types present in the seed fields; contamination cue to mechanical mixtures at time of sowing , harvesting, threshing, processing & handling of seeds and contamination due to seed-borne diseases from near by fields. Protection from these sources of contamination is necessary for maintaining genetic purity & good quality seed. Isolation is required during raising of a seed crop to avoid contamination due to natural crossing & disease infection, by sowing, harvesting, threshing and handling of seeds to avoid mechanical mixtures. d) Roguing Of Seed Fields: The existence of off type plants, i.e. plants

differing in their characteristics from those of the seed variety is another potent source of genetic contamination. Although a low %age of such plants may not seriously jeopardize the genetic purity of the variety, their

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continued presence would certainly deteriorate the genetic purity of the variety. The removal of such plants is referred to as roguing. There are three main sources of off type plants. Firstly the off type plants may arise due to presence of some recessive genes in homozygous conditions at time of release of varieties. The recessive genes may also arise by mutation. The heterozygous plants segregate from the characters affected by the particular gene in later stages of production cylces & give rise to off types. Another source of off type plants is the volunteer plants arising from accidentally planted seeds or from seed produced by earlier crops. For this reason the fields for producing seed of a particular variety should not have grown a potentially contaminating variety for a specified no: of preceding years. Mechanical mixtures as described earlier also constitute the major source of breakdown in genetically homogeneity. Off type individual plants should be rouged out of seed production fields before pollination occurs. Regular supervision by trained personnel is imperative. In other instances it may be necessary to control certain seedborne diseases. e) Seed Certification: The genetic purity in commercial seeds production is

often maintained through a system of seed certification. The principal objective of seed certification is to maintain & make available crop seeds, tubers or bulbs and some times turf grasses which are of good seeding value and true to variety. To accomplish these purposes, qualified & well experienced personnel of seed certification agency carry out field inspections at appropriate stages of crop growth. They also make inspections to that the seed crop/seed lot is of the requisite genetic purity & quality, after harvesting to quality & at the processing plants draw samples for seed testing & sometimes for grow out test also. In addition to inspection seed certification agency also lay down the field & seed standards to which the seed crop & seed lot respectively must conform to get approval as certified seed. The field standards include land requirement, isolation requirements maximum permissible off type shedding tassels (in case of hybrid maize program) etc. f) Grow-out Test: Varieties being grown for seed production should

periodically be tested for genetic purity by grow-out tests, to make sure that they are being maintained in their true form.

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AGRONOMIC PRINCIPLES Standardized seed production, besides genetic principles involves the application of the following agronomic principles to preserve good seed quality & abundant seed yields. Selection of a Suitable Agro-climatic Region A crop variety to be grown for seed production in an area must be adapted to the photoperiod & temperature conditions prevailing in that area. The crop varieties sensitive to photoperiodism & temperature should be grown in selected localities where these could be economically produced. Regions of moderate rainfall & humidity are much more suited to seed production than regions of high rainfall & humidity. Most crops require a dry sunny period & moderate temperatures for flowering & pollination. Excessive dew & rain cause hindrance in normal pollination resulting in poor seed set. Similarly too high temperature causes desiccation of pollen resulting in poor seed set. If hot dry weather conditions prevail during flowering, many crops such as vegetables, legumes & fruit trees fail to set seed effectively & produce many seedless fruits. The crops invariably require cool conditions with low atmospheric humidity to flower & pollinate normally. In wind pollinated crops bright sunny weather with gentle winds which cause an even flow of pollen over crop during flowering is conductive to best pollination & good seed set. Though other crops e.g. oil crops can withstand hot periods during flowering, but very high temperature results in premature flowering & production of poor quality seeds. Similarly very cold temperatures may also damage seed quality especially in the early phases of seed maturation. In general regions with extreme summer heat & very cold winters should be avoided for seed production unless particular crops are especially adapted to grow & produce seed under these conditions. Apart from complicating pollination, excessive rainfall leads to a higher incidence of diseases & makes seed harvesting extremely difficult. It may also result in delayed maturity & pregermiantion of seed in many standing crops. As the seed crop approaches maturity it becomes increasingly susceptible to shattering. Strong winds & heavy rainfall at or near harvest time may cause heavy seed losses particularly in crops which have a tendency to shatter their seed readily. Such conditions may also complicate the harvesting & subsequent harvesting operations. It is therefore clearly evident that ample sunshine, relatively moderate rainfall & the absence of strong winds have decided advantages for

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productive & high quality seed production & must be kept in view in the selection of areas for seed production. Selection of Seed Plot The plot selected for seed crop must have following characteristics:a) Soil texture & fertility of plot should be according to the requirement of the seed crops. b) The seed plot should be free from volunteer plants, weed plants & other crop plants. c) The soil of the seed plot should be comparatively free from soil-borne diseases & insect pests. d) In the preceding season the same crop should have not been grown on this land, if it is so required by seed certification standards. e) It should be feasible to isolate the plot as per requirements of certification standards. Isolation of Seed Crop The seed crop must be isolated from other nearby fields of the same crop & other contaminating crops as per requirements of certification standards. The isolation of a seed crop is usually done by providing distance between seed fields & contaminating fields. In hybrid maize seed production if the distance isolation is not feasible for nay reason, instead time isolation could be provided. Even the distance isolation requirement could be reduced in certified maize seed production by planting additional border rows. On a small scale i.e. in nucleus/breeder’s seed production the isolation can also be provided by enclosing plants or group of plants in cage or enclosing individual flowers or by removing male flower parts & then individual artificial pollination. After seed crop has been harvested isolation of seed produced of different varieties is necessary to avoid mechanical contamination. Similarly bags or other containers used to hold the seed must be carefully cleaned to remove any seed which may have remained in the bags from previous lots. Preparation of Land The land for seed crop must be prepared well. Good land preparation helps improved germination, good stand establishment & destruction of potential weeds. It also aids in water management & good uniform irrigation.

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Selection of Variety The variety for seed production must be carefully selected. Except in exceptional cases it should satisfy the following criteria’s: a) The variety should be adapted to agro-climatic conditions of the region. b) The variety should really be high yielder. c) The variety should posses other desirable attributes, namely disease resistance, earliness, grain quality. Seed The seed used for raising a seed crop should be of known purity, appropriate class & invariably obtained from an authorized official agency. While buying the seed the following factors should be carefully examined: a) That the seed of the appropriate seed class is bought for raising a foundation seed crop, seed of the breeder’s seed class is required & for raising a certified seed crop the seed of the foundation seed class is required for sowing. b) That the tag & seals of the breeders/foundation seed bags purchased are intact. c) That the validity period has not expired. d) That all the bags are of the same variety. Seed Treatment The seed may require seed treatment before planting, if they are not already appropriately treated. This could be easily done with help of a revolving drum at the farm. Depending upon the requirement one or more of the following seed treatments may be given: a) Chemical seed treatment. b) Bacterial inoculation for legumes. c) Seed treatment for breaking dormancy due to hard seeded ness. Time of planting The seed crops should invariably be sown at their normal planting time. Depending upon incidences of disease & pests, some adjustments could be made if necessary. At time of planting there should be sufficient soil moisture for germination to take place. Seed Rate Lower seed rates than usual for raising commercial crop are desirable because they facilitate roguing operations & inspection of seed crop.

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Method of Sowing The seed crops should be sown in rows with the exception of thickly sown crops where the sowing could be done by broadcasting. The most efficient & ideal method of sowing is by mechanical drilling, as it allows the deposit of the seeds in desired amount at uniform depth. It is of utmost importance to ensure that the seed drills/planters are absolutely clean, i.e. free from left over seeds of other crops. The sowing of seed crops in rows helps in conducting effective plant protection measures, roguing operations & field inspections. For many crops spacing within row is often more important than distance between rows, close spacing in row usually stimulate fibre & oil crops to branch more profusely at top & produce more seeds. For herbage crops too especially grasses adequate space for the penetration of air & sunlight to reach developing inflorescence at the base of the plants appear to be of special importance. For hybrid planting of two parents namely female parent line & male parent line has to be done in a definite proportion 4:2 or 6:2. It is imperative to ensure that the seeds of male & female parent line do not get mixed while planting. After planting of the male & female lines six to eight border rows of the male parent may also be sown if required. After sowing male rows should be marked to facilitate later operations. Depth of Sowing Depth of sowing is extremely important in ensuring a good plant stands. Small seed should be usually be planted shallow, but larger seeds could be planted a little deeper. Seeds would emerge from greater depths in sandy soils than in clay soils and also in warm soil as compared to cold. In dry soils seeds should be planted slightly deeper as so that they come in with moisture. Roguing Adequate & timely roguing is extremely important in seed production. As mentioned earlier the rogue which differ from normal plant population in being weak or sickly or bolters or dissimilar may cause quick deterioration in seed stocks by crosspollination, transmission of diseases etc. they should therefore be removed at earliest possible date before flowering. It is wise to remove the whole plant and not just the flower head. The no: of roguings necessary will vary with the crop, cleanness of planting seed & stage of the multiplication of the seed crop.

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Roguing in most of the field crops may be done at any of the following stages as per needs of the seed crop. a) Vegetative /preflowering stage b) Flowering stage c) Maturity stage Supplementary Pollination Provision of honey bees in hives in close proximity to the seed fields of crops largely cross-pollination by insects, ensure good seed set & thereby greatly increase seed yields. Weed Control Good weed control is a basic requirement in producing good quality seed. Weeds may cause contamination of the seed crop in the following ways in addition to reduction in yield: a) The presence of weed seeds at time of crop harvest leads to mixing of weed seeds with crop seeds. In many instances it is difficult to remove them during the processing of seeds. b) The presence of weeds in the seed field or nearby areas may serve as host to no: of diseases. Good & effective weed control therefore would be necessary to obtain good seed yields & to avoid contamination. Disease & Insect Control Successful disease & insect control is another important factor in raising healthy seed crops. Apart from reduction in yield, the quality of seeds from disease & insect damaged plants is invariably poor. Poor disease & insect control affects seed quality in the following three ways:a) There are a no: of diseases which are systemic. If these are not checked the seed produced will get infected with spores of such diseases & produce diseased plant in next season. b) There are certain diseases which are not systemic, leave their spores on seed coats. If not checked this results in a greater susceptibility to various seedling diseases which can affect the crop. c) Seed yield & quality are reduced. Following principles may be adhered for an effective management of diseases & pests in seed crops:a) Plant only treated seed. b) Prepare & adopt appropriate schedule of spraying for effective disease & insect control. 11

c) Roguing of diseased plants & ear heads from time to time also helps in checking the further spread of diseases. Nutrition In the nutrition of see crops nitrogen, phosphorous potassium & several other elements play an important role for proper development of plants & seeds. It is therefore advisable to know & identify the nutritional requirements of seed crops & apply adequate fertilizers. Adequate fertilization results in maximum yields, god seed quality & better expression of plant type which facilitate roguing & thereby helps in maintaining higher genetic purity as well. Irrigation It has been stressed earlier that comparatively dried regions are more suitable for good quality, disease free seed production. In such regions irrigation is essential to obtain good seed yields. The irrigations may be required before planting & at intervals upto flowering. One or two irrigations beyond flowering are desirable for may seed crop. In general lighter soils need more irrigation than heavier soils. Harvesting Of Seed Crops Time of Harvest: The optimum time of harvest is when the seed is fully mature, when weather damage has just begun & the seed is easily harvested & cleaned resulting in minimum harvest losses. Harvesting at earlier stages makes combining difficult & relative losses due to threshing & cleaning are greater. Similarly harvesting at a late stage may result in increased weather damage to seeds & losses due to shattering seeds & lodging of plants in the field. The optimum harvest time is somewhere between these two extremes. Method of harvesting: In India harvesting of crop is done by hands. This if done at appropriate time gives good quality of seed. However the subsequent quality of seed is dependent upon the handling of harvested crop & the care taken during threshing. Every effort should be made to avoid chance mechanical mixing, mechanical injury to seed during threshing. Lot identity should be maintained. If harvesting is done with combine & the seed crops are directly combined in the fields, threshing is not required. Precautions must be taken to adjust the combines properly so as to keep various losses & mechanical injury to seed during combining.

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Drying Of Seeds The seed lots are usually are at high moisture content at the time of harvesting & threshing. In order to preserve seed viability & vigour it is necessary to dry seeds to safe moisture content levels. Important precautions to be taken in this respect are: a) Identity of the lots must be maintained. b) Care should be taken to ensure that mechanical mixture does not take place. c) Drying of seeds to safe moisture limits should be done rather quickly. If the seeds are to be artificially dried they should be supplied to processing plants soon after harvesting. Storage of Raw Seeds The best method of storing seed for short period is in stacks or bags in ordinary building or godowns. After sun drying the seed should be filled in neat & clean bags. if old bags are to be used they should be properly cleaned & treated before use. Each and every bag should be marked appropriately. The stacks of bags should be made on wooden pallets. The godowns to be used for storage should be of seed should be dry, cool, clean & sprayed with malathion & later fumigated as & when necessary.

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